SiUS281117
Troubleshooting by Remote Controller
174
Service Diagnosis
Check for causes of drop in low pressure
Referring to the Fault Tree Analysis (FTA) shown below, probe the error points.
Note:
1: The “low pressure protection control” includes low pressure protection control and hot gas
bypass control.
2: In cooling, the indoor unit electronic expansion valve is used for “superheated degree control”.
3: In heating, the outdoor unit electronic expansion valve (EV1) is used for “superheated
degree control of outdoor unit heat exchanger”.
CHECK 2
Abnormally low
low-pressure
(Low evaporating
temperature)
[In cooling]
Defective
low pressure
control
Defective
compressor
capacity
control
Defective low pressure sensor
←
Are the electrical characteristics normal?
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
←
Are the electrical characteristics normal?
←
Are the coil resistance and insulation normal?
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
←
Are the coil resistance and insulation normal?
Defective service monitor PCB
Defective
low pressure
protection
control
Defective low pressure sensor
Defective hot gas solenoid valve
Defective service monitor PCB
[In both cooling
and heating]
(See
∗
1.)
[In cooling]
If the indoor unit
electronic
expansion valve is
throttled too much:
(See
∗
2.)
Defective indoor
unit electronic
expansion valve
Defective valve coil
Defective valve body
Defective
control
Defective
control
Defective gas pipe
thermistor of indoor unit
Defective liquid pipe
thermistor of indoor unit
Defective service monitor PCB
←
Check for the thermistor resistance and connection.
←
Check for the thermistor resistance and connection.
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
Defective outdoor
unit electronic
expansion valve
Defective valve coil
Defective valve body
←
Are the coil resistance and insulation
normal?
[In heating]
If the outdoor unit
electronic
expansion valve
excessively
throttled:
(See
∗
3.)
Defective low pressure sensor
Defective suction pipe thermistor
Defective service monitor PCB
←
Are the electrical characteristics normal?
←
Check for the thermistor resistance and
connection.
←
Is the suction air temperature not less than 57˚F
←
Is the indoor air temperature not less than 57˚F
[In cooling]
Low suction air
temperature of
the evaporator
[In heating]
Low suction air
temperature of
indoor unit
Short circuit
Low outdoor air temperature
Defective suction air thermistor of indoor unit
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←
Is the outdoor air temperature not less than 5˚F?
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
Low suction air temperature of outdoor unit
Defective outdoor air temperature thermistor of outdoor unit
High pipe
resistance
Abnormal piping length
Bent or crashed pipe
Clogging of foreign particles
Stop valve closed
←
Does the piping length fall in the permissible range?
←
Conduct visual checks for pipe conditions.
←
Is there any temperature difference caused before
and after the filter or branch pipe?
←
Check to be sure the stop valve is open.
Less
circulation
quantity of
refrigerant
Degradation
in condensing
capacity
Inadequate refrigerant quantity
←
Refer to troubleshooting "U0".
←
Eliminate moisture by vacuum operation.
←
Is the heat exchanger clogged?
Moisture choke
Dirty
evaporator
Decreased
fan airflow
rate
Decreased
fan output
Defective fan motor
←
Can the fan motor be rotated with hands?
Are the motor coil resistance and insulation normal?
Defective service monitor PCB
(Including capacity setting)
←
If a spare PCB is mounted, is the capacity
setting properly made?
←
Is the air filter clogged?
←
Is there any obstacle in the air passage?
High air
passage
resistance
Dirty filter
Obstacle
Defective electronic
expansion valve
control
